Low bit rate voice transmission for use in a noisy environment
First Claim
1. A method for processing an audio signal, comprising the steps of:
- digitizing an input signal that includes an audio signal component, a coherent noise signal component, and a non-coherent noise component;
applying the digitized audio signal to a linear predictor means, the linear predictor means having a plurality of serially coupled time delay elements wherein a time delay between adjacent time delay elements is selected for attenuating the coherent noise component of the input signal, said linear predictor means having a residual output signal that is representative of the audio signal component and the non-coherent noise component, less the coherent noise component;
applying the residual output signal to a synchronized overlap add processor means for compressing the audio signal component in accordance with a compression ratio, the synchronized overlap add processor means furthermore attenuating the non-coherent noise component of the input signal; and
further compressing the audio signal component with encoder means to provide a digital output signal that is expressive of the audio signal component.
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Accused Products
Abstract
A compressing a voice signal by the steps of (a) digitizing an input signal that includes a voice signal, the input signal including a coherent noise component; and (b) compressing the digitized voice signal with a synchronized overlap add processor (20). So as to prevent the synchronized overlap add processor from locking to the coherent noise component, the step of compressing includes an initial step of applying the digitized input signal to a linear predictor (16), the linear predictor having time constants selected for attenuating the coherent noise component of the input signal. The residual signal output of the linear predictor includes the voice signal, and an uncorrelated noise component if one is present in the input signal. The operation of the synchronized overlap add processor also functions to attenuate the incoherent noise component. Further compression of the compressed voice signal is accomplished by Huffman coding, arithmetic coding, or transform coding so as to provide a greatly compressed voice signal that, when subsequently expanded, is found to exhibit excellent voice quality.
177 Citations
17 Claims
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1. A method for processing an audio signal, comprising the steps of:
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digitizing an input signal that includes an audio signal component, a coherent noise signal component, and a non-coherent noise component; applying the digitized audio signal to a linear predictor means, the linear predictor means having a plurality of serially coupled time delay elements wherein a time delay between adjacent time delay elements is selected for attenuating the coherent noise component of the input signal, said linear predictor means having a residual output signal that is representative of the audio signal component and the non-coherent noise component, less the coherent noise component; applying the residual output signal to a synchronized overlap add processor means for compressing the audio signal component in accordance with a compression ratio, the synchronized overlap add processor means furthermore attenuating the non-coherent noise component of the input signal; and further compressing the audio signal component with encoder means to provide a digital output signal that is expressive of the audio signal component. - View Dependent Claims (2, 3, 4, 5)
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6. A method for compressing a voice signal, comprising the steps of:
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digitizing an input signal that includes a voice signal component to provide a digitized input signal, the digitized input signal further including a coherent noise component; and compressing the digitized input signal with a synchronized overlap add processor means, wherein, so as to prevent the synchronized overlap add processor means from locking to the coherent noise component, the step of compressing includes an initial step of applying the digitized input signal to a linear predictor means, the linear predictor means having a plurality of serially coupled time delay elements wherein a time delay between adjacent time delay elements is selected for attenuating the coherent noise component, said linear predictor means having a residual output signal that is representative of the voice signal component, less the coherent noise component, the residual output signal being applied to an input of the synchronized overlap add processor means for compression thereby. - View Dependent Claims (7, 8, 9, 10, 11)
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12. Apparatus for compressing a voice signal, comprising:
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means for digitizing an input signal that includes a voice signal component, the input signal further including a coherent noise component; and means for compressing the digitized input signal, said compressing means including a synchronized overlap add processor means, wherein, so as to prevent the synchronized overlap add processor means from locking to the coherent noise component, the apparatus further includes linear predictor means interposed between said digitizing means and said compressing means, said linear predictor means having a plurality of serially coupled time delay elements wherein a time delay between adjacent time delay elements is selected for attenuating the coherent noise component, said linear predictor means having a residual output signal that is representative of the voice signal component, less the coherent noise component, the residual output signal being applied to an input of the synchronized overlap add processor means for compression thereby. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification